BDHo

If a compression test shows compression loss at 10% across all cyclinders does this mean the car needs a top end? Its a 90k mile 993. What are other causes and perhaps fixes that do not require a $10k top end.
thanks so much

NP993

Compression test really doesn't test the valve guides, it tests the rings and valve seats. Oil consumption is really the only thing that tells you whether it needs a top end.

However, compression tests are often done incorrectly. The motor must be at or near operating temp. A compression test done correctly also rarely shows a perfectly consistent number across all cylinders. And comp tests don't measure compression loss, but the opposite.

It sounds to me like you're mixing up a leak down test with a compression test.

MarkD

10% loss? Compared to what?
Maybe you are saying there is a 10% variation?

What are the compression #s per cylinder?

Leakdown is more useful in determining engine health.
Neither comperession nor leakdown will tell you if the valve guides are worn.
Leakdown will tell where an issue is... exhaust valve, intake valve, rings...

FWIW, a top end refresh should not be $10K.

EDIT: Noah types faster than I do

BDHo

im sorry guys,
i meant leakdown is 10%.

race911

Uniformly 10% across all 6 cylinders? That would be odd. (The engine was at operating temperature, right?)

vincer77

A 10% leakdown is pretty marginal and indicates worn rings, or leaking valves. A good mechanic can usually tell if a valve is bad by listening if air is heard leaking through the intake or exhaust, but may require more teardown than usually done on a PPI. Does the car exhibit any other symptoms, i.e. low power, CEL etc...

NP993

10 percent leakdown on a cylinder should be detectable. Did the mechanic indicate where it was coming from? (rings, intake valve, exhaust valve)

If not, I would question this mechanic's skills. There is also no way that the motor has 10 percent leakdown on *every* cylinder. Or at least the odds of such an occurrence are very, very small...

raspberryroadster

agree with the above around 10% indicates issues/marginal top end.

do not just rely on leakdown, have compression tested as well - best sign of healthy engine - steady/close compression ratios across all cylinders

.....not a porsche but good overview
http://www.lextreme.com/leakdown.htm